25 research outputs found
Dispersive, superfluid-like shock waves in nonlinear optics
In most classical fluids, shock waves are strongly dissipative, their energy
being quickly lost through viscous damping. But in systems such as cold
plasmas, superfluids, and Bose-Einstein condensates, where viscosity is
negligible or non-existent, a fundamentally different type of shock wave can
emerge whose behaviour is dominated by dispersion rather than dissipation.
Dispersive shock waves are difficult to study experimentally, and analytical
solutions to the equations that govern them have only been found in one
dimension (1D). By exploiting a well-known, but little appreciated,
correspondence between the behaviour of superfluids and nonlinear optical
materials, we demonstrate an all-optical experimental platform for studying the
dynamics of dispersive shock waves. This enables us to observe the propagation
and nonlinear response of dispersive shock waves, including the interaction of
colliding shock waves, in 1D and 2D. Our system offers a versatile and more
accessible means for exploring superfluid-like and related dispersive
phenomena.Comment: 21 pages, 6 figures Revised abstrac
Exciton-polariton topological insulator
The authors thank R. Thomale for fruitful discussions. S.K. acknowledges the European Commission for the H2020 Marie SkĆodowska-Curie Actions (MSCA) fellowship (Topopolis). S.K., S.H. and M.S. are grateful for financial support by the JMU-Technion seed money program. S.H. also acknowledges support by the EPSRC âHybrid Polaritonicsâ Grant (EP/M025330/1). The WĂŒrzburg group acknowledges support by the ImPACT Program, Japan Science and Technology Agency and the State of Bavaria. T.C.H.L. and R. G. were supported by the Ministry of Education (Singapore) Grant No. 2017-T2-1-001Topological insulatorsâmaterials that are insulating in the bulk but allow electrons to flow on their surfaceâare striking examples of materials in which topological invariants are manifested in robustness against perturbations such as defects and disorder1. Their most prominent feature is the emergence of edge states at the boundary between areas with different topological properties. The observable physical effect is unidirectional robust transport of these edge states. Topological insulators were originally observed in the integer quantum Hall effect2 (in which conductance is quantized in a strong magnetic field) and subsequently suggested3,4,5 and observed6 to exist without a magnetic field, by virtue of other effects such as strong spinâorbit interaction. These were systems of correlated electrons. During the past decade, the concepts of topological physics have been introduced into other fields, including microwaves7,8, photonic systems9,10, cold atoms11,12, acoustics13,14 and even mechanics15. Recently, topological insulators were suggested to be possible in exciton-polariton systems16,17,18 organized as honeycomb (graphene-like) lattices, under the influence of a magnetic field. Exciton-polaritons are part-light, part-matter quasiparticles that emerge from strong coupling of quantum-well excitons and cavity photons19. Accordingly, the predicted topological effects differ from all those demonstrated thus far. Here we demonstrate experimentally an exciton-polariton topological insulator. Our lattice of coupled semiconductor microcavities is excited non-resonantly by a laser, and an applied magnetic field leads to the unidirectional flow of a polariton wavepacket around the edge of the array. This chiral edge mode is populated by a polariton condensation mechanism. We use scanning imaging techniques in real space and Fourier space to measure photoluminescence and thus visualize the mode as it propagates. We demonstrate that the topological edge mode goes around defects, and that its propagation direction can be reversed by inverting the applied magnetic field. Our exciton-polariton topological insulator paves the way for topological phenomena that involve lightâmatter interaction, amplification and the interaction of exciton-polaritons as a nonlinear many-body system.PostprintPeer reviewe